Signaling system



Sept. 4, 1945. K.- PFLEGER SIGNALING SYSTEM Filed June 4, 1943 3 Sheets-Sheet l lwa CHQ QQ VATTORNEY K. W. PFLEGER SIGNALING SYSTEM 5 Sheets-.Shet 2 Filed June 4, 1943 NIII.

, lick K. W PFLEGER BV Sept. 4, 1945.

Patented Sept. 4, 1945 SIGNALING kSYSTEM Kenneth W. Pfleger, Arlington, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 4, 1943, lserial No. 489,612

7 Claims.

This invention relates to signaling systems and particularly to signaling in systems comprising selectively operated switching devices.

Objects of the invention are the extension of the range of selective signaling, minimization of interference from longitudinal line disturbances, and the elimination of adverse effects from differences in earth potential in grounded signaling circuits. Other objects are an increase in the rapidity with which selective signals are transmitted and the provision of simple and ei'cient selective signaling means.

A feature of the invention is a signaling system in which a plurality of selective signals are transmitted by combining a selective variation of the impedance angle in grounded signaling circuits with a selective variation of the magnitude of the current in loop signaling circuits, the number oi signals thereby obtained being sufficient for the selective control of switching devices such as are ycommonly used in automatic telephone systems.

Another feature of the invention is a signaling system in which signal receiving means is selectively responsive to a variation in the impedance angle of one or more grounded signaling circuits and a variation in the magnitude of direct current in a loop signaling circuit.

A clear and complete understanding of the invention and its feature will be facilitated by considering specific embodiments of the invention represented schematically in the drawings which forms a part of this specification. The invention is not limited in its application to the systems shown in the drawings but is generally applicable to any system in which a plurality of selective signals are transmitted in grounded and loop circuits.

Referring now to the drawings:

Fig. l shows a telephone system comprising a subscribers station AI and line LI, a line finder switch LFI, district selector DSI, final selector FSI, and a called subscribers station B. Fig. l further shows a selective signal receiver SRI for receiving selective signals transmitted from the calling subscribers station.

Fig. 2 shows a telephone system similar to that shown in Fig. 1 with modified signal transmitting and signal receiving arrangements; and

Figs. 3 and 3A show the structure of the signal transmitting means provided at the subscribers station A in Fig. 1.

The line nder and selector switches shown in Figs. l and 2, may be of the Well-known panel type, the selector switches being revertively controlled by a register sender. Reference may be to the patent to Steam et al. No. 1,395,977 of November 1, 1921, and the patent to Stearn et al. No. 1,505,171 of August 19, 1924, for a disclosure of systems comprising register sender controlled panel type switches. The subscribers fill stations are of the type usually provided in common battery systems. vStation AI is provided with a key-set mechanism for transmitting selective signals. This mechanism which is shown in detail in Figs. 3 and 3A consists of a set of twelve keys, any desired one of which may be operated to transmit a selective signal over the subscribers. line to the `central office. To transmit the ofce codey and number of a called subscribers line, the required key is operated for each of these digits in succession. Uponoperation of a key for the transmission of the Vfirst digit of the oiiice code, the key-set contacts ||5 and -IIGA are actuated'to disconnect the telephone set from the line conductors-IM and |02; the contactv II I is actuated to connect ground through retard coil H3' and condenser III A-to conductor |0I; and the contact |I8vis actuated to connect ground through retardvcoily I I4 and condenser I|2 to `conductor |02.V The `operation of each of the twelve keys causes theoperation of a different combination of contacts |03, |05, |08, |09 and ||0. The actuation of contact |03 is effective to close a short-circuit across lthe conductors |0| and |02; the actuation offwntact |05 is effective to connect the resistor |04 across conductors |0| and |02; the actuation of contact |08 is effective to bridge theresistor, |06 and inductance |0'I in series across conductors |0| and |02; the actuation of contact |09 iseiective to short-circuit the retard coil ||3; andthe actuation of contact ||0 is eiective to short-circuit the retard coil. ||4. The particular contacts |03, |05, |08, |09 and I|0 which are operated by the depression of a digit key are restored t0 normal when the key is released; but contacts ||5, ||6, ||'|k and IIS. remain in actuated position until all of the digits required for completion of the connection have been transmitted.

Referring to Fig. 3, the frame 300 forms a support for the keys3|0 and mechanism actuated by operation of the keys, only one of which is shown. The upper portion of frame 30G-,forms a cradle to receive the telephone handset when not in use.- When the handset isin the cradle, the pin 30| is depressed against the-tension of spring 302 to actuate the contact springs 305 to disconnect the handset from the conductors of line LI in the usual and well-known manner. Each of the twelve keys 3 0 has associated therewith a push-bar 3|| which is pivoted on a rod 3|2, the opposite end of each push-bar being in engagement with a cross bar 3|6 extending between two end bars 3||, as shown in Fig.3A. Each push bar 3|| and key 3|0 are normally held in non-operated position, as shown in the drawings, by a spring 3|3. The end bars are pivoted on the rod 3|8 and are held in normal position by springs 3|9. push-bars 3|| has its under-surface formed to actuate one or more sets of contact springs which Each of eleven of the` are individual thereto, the springs being numbered |03, |05, |08, |03 and ||0, depending upon the position of the' projection on the push-bar by which it is actuated. For instance, the bar 3| I, shown in Fig. 3, has a projection 3|4 for actuating contact springs I| and a projection 3|5 for actuating springs |09. eleven bars has a diierent combination of projections and contact springs actuated thereby, the contacts actuated by the similarly located projections of different push-bars being connected in parallel so that each of the contacts numbered |03, |05, |08, |09 and IIO in Fig. 1 represent all like-numbered sets of contact springs individual to the push-bars 3| I. The push-bar 3|| associated with the twelfth key has no projections or sets of contacts associated therewith. Thus, the depression of any of eleven of the keys actuates the corresponding push-bar to close a particular combination of contacts |03, |05, |08, |09 and ||0; and the depression of the twelfth key actuates the corresponding push-bar but does not actuate any of these contacts. The actuation of each of the twelve push-bars moves the cross bar 3I6 and end bars 3|1 on the pivot rod 3| 8 and against the tension of springs 3|9. The free end of the end bar 3|I shown in Fig. 3 carries a flat spring 320on the upper end of which is mounted an actuating member 32 I. The lower end of the actuating member 32| forms a driving pawl 322 which engages the teeth 323 of a driving wheel 324. The upper end of the actuating member 32I engages a bearing surface 340 which is formed by or attached to the frame 300. The toothed wheel 324 and a cam wheel 330 are rotatably mounted on a xed shaft 328. The cam wheel is attached to the toothedwheel and a clock spring 329 is effective to maintain both wheels in normal position with the projection 33| of cam wheel 330 in engagement with the stop 34| of the frame 300. With the wheels in normal position, the cam surface 332 engages the contact spring actuating bar I I9 to close contacts and IIS and open contacts |I1 and |I8 of the spring pile-up |20. Each actuation of the end bar 3| I by the depression of a key 3|0 is effective to rotate the toothed wheel 324 and cam wheel 330 one step. When the key 3|0 which has been depressed is released, the end bars 3|'I resume their normal position1 but the toothed wheel 324 and cam wheel 330 are held in their advanced position by the retaining pawl 325, the pawl 325 being pivoted at 326 and held in engagement with the wheel 3-24 by a spring 321.

As soon as the cam wheel 330 is advanced out of normal position by the movement of the end bars 3|I responsive to the depression of a key 3|0 corresponding to the rst digit of a called ofce code, the cam controlled spring actuating bar I I9 moves to the right thereby opening contacts II5 and ||6 to disconnect the calling subscribers telephone set from the conductors of line LI and closes the contacts II'I and I|8 to close a separate signal transmitting circuit :over each of the line conductors III and |I2. The actuation of a key 3| 0 for each succeeding digit of theA called office code and called subscribers number eects an advance of the toothed wheel 324 and cam wheel 330 one step; and, at the same time, a combination of the contacts |03, |05, |08, |09 and I|0 is actuated to selectively transmit the desired digit. When all of the digits of the oflice code and called subscribers number have been transmitted by a corresponding number of key operations, the cam wheel 330 'will have been ad- Each of these` vanced to a position in which the cam surface 332;.has again engaged the contact actuating bar H9, thereby to open the selective signaling circuits over conductors |0I and |02 and connect the subscriber telephone set to these conductors for talking. The wheels 324 and 330 remain in this off-normal position during conversation. When the handset is replaced in the cradle at the end of the call, the actuating element 303, which is integral with or carried by the pin 30|, bears against the actuating element 32| and also against a projection of the retaining pawl 325 whereby the driving pawl 322 and the retaining pawl 325 are disengaged from the wheel 324. The spring 329 rthereupon drives the two wheels 324 and 330 back to their normal position, with the projection 33| resting against the stop 34| and with the cam surface 332 engaging the contact actuating element `I I9.

The signal receiver SRI 'shown in Fig. 1 forms part of a register sender which registers the digits of a called subscribers oiiice code and number and controls the operation of the selector switches through which a talkingv connection is established between the'calling and called lines. It is assumed that the register sender, of which the signal receiverSRI forms a part, is connected to conductors I 2| and |22 upon connection of the calling line to these conductors by the operation ofthe line finder switch LFI. Dial tone is thereupon transmitted to the calling station in the usual manner tov indicate that the keys of the subscribers key-set may be operated to selectively transmit the called office code and number. When the calling subscriber depresses the key corresponding tothe first digit of the called oice code, the cam controlled actuating elementl I9 eects the opening of contacts I|5 and IIB whereby relay means in the register sender, which means is not shown in the drawings, is operated to disconnect the dial tone and to connect the signal receiver SRI to conductors I2I and |22 for response to each of the digit signals transmitted by operation of the calling subscribers key-set.

The signal receiver SRI comprises polarized relays |25, |25 and |21 connected in series with an antirescnant network |23, a non-grounded battery |28 and a resistor |29 across conductors |2I and |22; and these relays are operatively responsive to the selective closing of direct current loop circuits over line LI. The signal receiver SRI also comprises a source GI of alternating current of suitable frequency, for instance cycles, hybrid coils I'I0, III, I'I2, |3| and |5I, series resonant `networks |30 and |50, comprise networks |33 and |53, attenuation pads |38 and |53, phase shifters |39 and |59, phase detectors DI and D2 and differential relays |49 andl |69 for responding to the selective closing of separate grounded alternating circuits over the conductors of line LI. The signal receiver SRI further comprises register control relays ISI, |92, |93, |94 and |95 operatively controlled by relays |25, |25, |21, |49 and |69, and a group of twelve registers for each digit to be registered, only one register RI of one group being shown in the drawings. The transfer of the register control relays from one group of registers to the next may be effected in any desired known manner.

Each of the polarized relays I 25, |26 and |2I has a normally energized biasing winding which tends to maintain the armature in normal position as shown in the drawings. The operation of key-controlled contact |08 connects resistor I ucts.

|04, resistor |06 and induction coil |01 across conductors and |02 in series with the upper windings of relays |25, |26 and |21 and the battery |28. The impedance of elements |04, |06, and |01 is high enough to prevent the operation of marginal relays |26 and |21, but relay |25 is sensitive enough to be operated by the current in the circuit closed by contact |08. The operation of key-controlled contact |05 connects resistor |04 across conductors I9| and |02, the current through the operating windings of relays |25, |26 and |21 being sufficient to effect the operation of both of relays and |26 but insufficient to effect the operation of relay |21. The operation of key-controlled contact |03 closes a short-circuit across conductors I0| and |02 thereby to effect the operation of all three of relays |25, |26 and |21. Thus, there are three direct current signaling conditions which may be selectively and independently established at the calling station and recognized by the signal receiver.

The resistors |13, |31 and |51 are selected to balance the impedance of the input circuits of the hybrid coils |10, |1| and |12, respectively. The attenuation pads |38 and I 58 may be omitted if the hybrid coils I1| and |12 are well balanced. The network |23 is antiresonant at the frequency of source GI to prevent the transmission of alternating current through the windings of relays |25, |26 and |21. The networks |30 and |50 are resonant at the frequency of source GI to permit the transmission of signal current therethrough to the line conductors |0I and |02; and these networks do not pass direct current. 'Ihey attenuate any interference currents such as power line hum, transients or modulation prod- The networks |33 and |53 are designed for lines of average length, and the values of the elements |34, |35, |36 and |54, |55, |56 are such that the voltage across the upper windings of transformers |42 and |62 has a positive angle when the corresponding one of inductances 3 and |I4 is short-circuited by the closure of keycontrolled contact |09 or ||D at the calling station and has a negative angle when the corresponding one of these inductances is not shortcircuited. Each of the phase detectors DI and D2 comprises a first input transformer |4| or ISI, a second input transformer |42 or |62, balanced push-pull vacuum tube rectiers |45 and |46 or |65 and |66, and a differentially wound. polarized relay |49 or |69. It is possible to replace the vacuum tubes with other types of rectifier, for instance copper oxide rectiers. It is also possible to replace each of the phase detectors with a dynometer type relay. The voltages in the right windings of the transformers |4| and |6| are adjusted in phase to have the desired phase angle with respect to an arbitrary standard voltage having zero angle. The phase Shifters |39 and |59 are of known form and may provide for both Xed step and continuously varying adjustments; and. if necessary a switch may be provided in each of the phase shifters for interchanging the input leads to the phase detectors in which case a S60-degree phase adjustment is possible. The amplitude of the voltage applied to the input side of transformers I4| and I6| of the phase detectors is controlled by the setting of the variable resistor |46 or |60. With the phase shifter |39 properly adjusted, the voltage applied to the rectiflers of phase detector D| will be effective to energize relay |49 to close its right contact when the phase angle of the voltage in the upper winding of transformer |42 is positive and to maintain closure of the left contact when the phase angle of the voltage in the upper winding of transformer |42 is negative. Thus, relay |49 closes its left contact when keycontrolled contact |09 is normal and inductance coil I3 and condenser are in series with conductor I0|; and relay |49 closes its right contact when Contact |09 is closed and coil ||3 short-circuited. With the phase shifter |59 properly adjusted, the voltage applied to the rectiers of phase detector D2 will be effective to energize relay |69 to close its right contact when the phase angle of the voltage in the upper `wind ing of transformer |62 is negative and to maintain closure of the left contact when the phase angle of the voltage in the upper winding of transformer |62 is positive. Thus, relay |69 closes its right contact when key-controlled contact ||0 is normal and inductance I4 and condenser |42 are in series with conductor |62; and relay |69 closes its left contact when contact ||0 is closed and coil ||4 is short-circuited. Thus, there are four alternatingi'current signal conditions obtainable between the key-set at the calling station and the signal receiver SRI, as follows: (1) with both of key-controlled contacts |09 and H6 normal, in which case coil I|3 and condenser I|I are in series with conductor |0| and relay |49 is normal; and coil ||4 and condenser ||2 are in series with conductor |02 and relay |69 is normal; (2) withboth of contacts` |09 and |||J closed; in which case coils |3 and I I4 are short-circuited and both of relays |49 and |69 are operated;

(3) with contact |09 closed and contact H0 normal, in which case coil ||3 is short-circuited and relay- |49 is operated and coil ||4 and oondenser II2 are in series with conductor |62 and relay |69 is normal; and (4) with contact |09 normal and contact I I9 closed, in which case coil II3 and condenser I|I are in series with conductor |0I and relay |49 is normal and coil ||4 is short-circuited and relay |69 is operated.

Interference currents in the conductors of line LI, although considerably attenuated by the series resonant networks '|30 and |50, the compromise networks |33 and |53 and the hybrid coils |3| and |5I, will pass in equal volume into theY rectiers |45 and |46 and in equal volume into the rectifiers |65 and |66, both windings of each of dierential relays |49 and |69 being thereby energized in opposition without operative effect. Since current of the signaling frequency from source GI appears in the input transformer |4| and also in the input transformer |42, there will be some modulation products at the rectifier outputs corresponding to the sum and difference frequencies between the interference frequency or frequencies and the signaling frequency; and these modulation products will produce beats. If the signaling frequency is 10() cycles per second and the interference current is 60 cycles per second, the beats may be in the order of 40 cycles per second in which case the differential relays |49 and |69 should be sensitive only to frequencies below 40 cycles per second, this result being obtainable by making these relays somewhat slow to respond although capable of satisfactory response to key closures at the rate of l0 cycles per second. To further protect against interference from beats produced by modulation products and the signaling frequency, band-pass lters |43 and |63 may be inserted in series with the input side of transformers |42 and |62,

' whereby current of only the signaling frequency ancl"its sidebands is applied through trans-` formers |42 and |52. If the signaling frequency is 100 cycles per second, the band passed by these filters might be 85 to 1'15' cycles per' second' thereby clearing out all interference from 25 or 60- cycle per second current and from harmonics of these frequencies with the possible exception of the fourth harmonic of 25-cycle current.

Each of the alternating current signaling conditions may be established simultaneously with the above-described direct current signal conditions providing the coupling introduced. between the two conductors of the line by closure of the direct current circuit is not sufcient to interfere with the selective response of relays |49 and |89. The coupling introduced by the operation of key-controlled contact |08 is not suicient to effect the response of relays lg'and |59 since the impedance of elements |00, |06 and` |01 is high; and therefore the direct current signaling condition produced by the closure of contact I {iS-may be combined with each of the aforementioned iour alternating current signal conditions. The inductance coil |01- may be omitted if the line is not too long, thereby enabling faster direct current signaling. Whenever the coil |01 is provided, its direct current resistance is included in the value of resistor in computing its effect. The alternating current resistance of coil |91 should be high so as to permit a small sized core. Since the operation of each of keycontrolled contacts |03 and |05 produces a close coupling between the conductors of line L|', it is not possible to combine the direct current signal conditions selectively produced by the closure of each of these contacts with each of the four alternating current signal conditions. But each of these two direct current signal conditions may be combined with the alternating current signal condition which exists when neither of key-controlled contacts |09 and H0 is closed and also with the alternating current signal condition which exists when both of key-controlled contacts |09 and ||0 are closed; because, in either of these cases, the alternating current potentials are balanced all along the conductors |0| and |02. Thus, there is a total of twelve non-interfering signal conditions which may be selectively established under the control-of the key-set at the calling station to effect registration of any called subscribers ofce code4 and number in the register sender which controls the operation of selector switches through which the desired connection is established. These twelve signal conditions are clearly indicated by the following table:

The register control relays |9| to |95 are controlled by relays |25, |26, |21, |49 and |69 to operate the corresponding. registers. A separate relayor other electromagnetic device, such as Rh may beV provided for each value of each digit; or a groupv of relays may be provided for each digit, the particular combination of relays being actuated which represents the value of the digit keyed. f Since it may be desirable to use a decimal code and to provide for the operation of a supervisory relay to hold the connection between the calling line and the register sender while keying'is taking place, the rst signal condition ofthe table would not be used and another of the twelve possibleisignal conditions, for instance the eleventh, would be utilized as the condition existing between the depression of a key to transmit one, digit and the depression of a key to transmit the next digit of the called oiice code and subscribers number.

'A modication of the arrangement shown in Fig. 1 consists of the omission of contact springs |03 and they omission of the ratchet and cam wheel mechanism. When the subscriber removes the handset, the line L| is extended through a line finder switch LF and a link (not shown) to an idle register sender in the usual manner, all of contacts |05, |08, |00, H0, ||1 and ||8 being open and contacts ||5 and ||6 being closed to admit dial tone to' the handset. Thedial tone is of a high enough frequency, for instance 1,000 cycles, that it does not interfere with the direct or alternating current signaling conditions. All of the direct current controlled signal relays |25, |28 and |21' are operated while contacts 5 and H5 are closed Linder which condition no registration is` effected in the register sender. The depressionof any key effects the opening of contacts ||5 and ||6 and closes a particular combination of contacts |05, |08, |09, H0, ||1 and H8. The opening of contacts ||5 and llt`r always effects the release of relay |21 thereby rendering the register control relays effective to register the digit being transmitted. Ten signal conditions are possible, these conditions being the same as the rst ten of the above table.

A preferred embodiment of the invention, which requires only one phase detector, is shown in Fig. 2.l The signal transmitting means at the subscriber's station comprises ten push-button keys, key-controlled contacts 203, 204, 205, 201, 209, 2|| and 2|3, condensers 20S and 208, resistor 2|0 and inductance coil 2|2. The signal receiver SR2 comprises two marginal relays 23| and 232 and a polarized relay 240 for responding to direct current signal conditions established by operation of certainof the digit keys at a connected calling subscribers station. The signal receiver SR2 also comprises a source G2 of alternating current of desired frequency, for instance cycles per second, hybrid coil 241 for impressing the voltage of source G2 on both conductors of the calling line, a phase detector D, and phase and volume control means 249 and transformers 245 and-246 connecting the phase detector to the conductors of the calling line. The phase detector D comprises input transformers 250 and 25|, vacuum tube rectiers 255 and 255 and differential polarized relay 259. The signal receiver SR2 further comprises register control relays 21|, 212, 213, 214, 215 and 219 for effecting the operation of the digit registers under the control of the signal relays 23|, 232, 250 and 259. The antiresonant networks 235 and 236 prevent false operation of relays 23|, 232 and 240 due to alternating current from source G2. When the line is balanced,` there is no current through the left coil of input transformer 250. The windings of a supervisory relay may be connected in series with coils :231 and 238 to maintain the connection between the calling line and the register 'sender while the called oice code and subscribersnumber are being transmitted.

When the subscriber at station A2 removes the handset, means, including a liney iinder LF2, is operated to connect the line L2 to anidle register sender which includes a signal receiver SR2. The dial tone may consist of current from source G2 or a separate dial tone source of higher frequency may be provided. Y At this time, keycontrolled contact 2I3 is closed but all of contacts 203, 201|,A 205, 201, 209 and 2II are open. The :direct current through the windings of relays 23| and 23-2 and battery 230 effects the operation of these relays; but, the line being balanced, relay 240 remains normal with its armatures in mid-position, and so also does relay 259 since there is no alternating current from source G2 through the left winding of coil 250. Longitudinal noise currents which exist at this time produce substantially equal and opposite voltages in the secondary windings of transformers 245 and 246 so that there is no input applied to transformer 25|. 'I'hese longitudinal noise currents do not aiect relay 240 since condensers 233 and 234 constitute a low impedance shunt for the windings of relays 23|, 232 and 2150 with respect to such currents. lWhile insulation leakage between one conductor of lineA L2 and ground will unbalance the line, the unbalance introduced by the normal allowable leakage will notbe suincient to cause operation of either one of relays 240 and 259.

The closure of key-controlled contact 203 con*- nects ground to conductor 202 andywith contact 2|3 open, relay v23| releases, relay 232 is held operated, and the line is unbalanced to effect the energization of relay 240 in a direction which closes its upper contact and to effect the energization of relay 259 in a direction which closes its left contact. The closure of contact 204 connects ground to conductor 20| and, with contact 2|3 open, relay 23| is held operated, relay 232 releases, and the line is unbalanced to effect the energization of relay 240 in a direction which closes its lower contact and to effect the energization of relay 259 in a direction which closes its right contact. The closure of contact 205 connects conductor 20.2 to ground through condenser 206; and, with contact 2|3 open, relays 23| and 232 release, relay 240 remains normal, and relay 259 is energized in the direction which closes its left contact. The closure of contact 201 connects conductor 20| to ground through condenser 208; and, with contact 2|3 open, relays 23| and 232 release, relay 240 remains normal and relay 259 is energized in the direction which closes its right contact. The closure of contact 209 bridges resistor 2|0 across conductors 20| and 202; and, with contact 2|3 open, relay 23| remains operated, relay 232 releases, and relays 240 and 259 remain normal. The closure of contact 2I| bridges inductance coil 2|2 across conductors 20| and 202; and, with contact 2|3 open,v relays 23| and 232 both remain operated, andY relays 240 and 259 remain normal. The opening ofcontact 2|3 without closing anyv of contacts 203, 204, 205, 201, l209 and 2|| causes the release of relays 23| and 232 and does not aiect relays 240 and 259. The selective operation of each of the ten digit keys effects the actuation of a different combination of the key-controlled contacts to control relays 23|, 232, 240 and 259; and relays 21| to 216, inclusive, are thereby controlled to pperate the corresponding registers. The following table indicates the various signal conditions and relays operated responsive to the depression of each of the ten digit keys, the two operated positions of each of the polar relays 240 and 259 being indicated by the letters M and S. The adjustment ofthese polar 'relays is different from that commonly used in that the tongues remain off contact when the relays are not operated.

Signal relays operated D k Ieyiol igit ey ro e operated contacts 259 240 closed 231 232 M S M S What is claimed is:

1. In a signaling system, a two-conductor line, a source of direct current and a marginal signal relay at one end of said line, said source and relay connected in series across the conductors of said line, signal sending means at the other end of said line for completing a circuit for operating said relay, an alternating current generator at said one end of said line, a network connected to one of the conductors of said line at said one end, means coupling said generator to said one conductor and network, a phase detector comprising balanced rectiers and a polarized relay, means coupling said generator to said detector, a transformer having a primary winding connested in parallel with said conductor and in parallel with said network and having its secondary winding connected in the input circuit of said recti'lers, means comprising an induction coil and a condenser connected in series with said conductor at said other end of the line, signal sending means for short-circuiting said induction coil, said polarized relay being energized in one direction when said inductance coil is included in the circuit through said conductor and energized in the other direction when said inductance s short-circuited, and signal register means selectively controlled by said marginal and polarized relays.

2. In a signaling system, a two-conductor line, a source of direct current and a marginal signal relay at one end of said line, said source and relay connected in series across the conductors of said line, signal sending means at the other end of said line for completing a circuit for operating said relay, an alternating current generator at said one end of said line, a network connected to one of the conductors of said line at said one end, means coupling said generator to said one conductor and network, a phase detector comprising balanced rectiers and a polarized relay, means comprising phase control means coupling said generator to said detector, a transformer having its primary winding connected in parallel with said conductor and in parallel with said network and having its secondary winding connected in the input circuit of said rectifier, means comprising an inductance coil and a condenser connected in series with said conductor at saidrotiher endof the line, signal sendingmeans for `shortcircuiting said inductance coil, said network and phase control means being .of sucha `character thatsaid polarized relay is energized in one direction when said induction coil is included in the circuit through said conductor and energized .in the other direction when said inductance is shortcircuited, andsignal register means selectively controlled by said marginal and polarized relays.

3. In a signaling system, a twoconductor line, a source of direct current, a plurality of signal relays including a marginal relay connected in series lWith said source across the conductors of said line, signaling means at the other end of said line for selectively completing circuits for selectively operating said relays, an alternating current generator at said one end of said line, a network connected to one of the conductors of said line at said one end, means coupling said generator to said one conductor and network, a phase detector comprising balanced rectiersand a polarized relay, means coupling said generator to said detector, a transformer havingV its primary Winding connected in parallel with said conductor and in`parallel with said network and having its secondary Winding connected in the input circuit of said rectiers, `means l.comprising an induction coil and 4a condenserconnected in series with said .conductor at said lother yend of the line, signal vsendingmeans ior short-circuiting said .induction poil, said polarized relay being energized in one direction .when said induction coil is included in a circuit through said conductor and energized in :the other direction when said inductance is short-circuited, and signal register means selectively controlled 'by said. mar' ginal and polarized relays.

4. In avsignaling systemfa line, .signal .receiving means connected. to one end Aof said line, signal transmitting means connected to Ithe other end of said line, said signal receivingmeanscomprising a source of direct current and-a pluralityA of signal relays connected '.in .seriesacross .the conductors ofV said line, Aone .of .said .relays .being a marginal relay, said signal .transmitting 4means comprising means for .closing a ldirect current circuit over said line to operate one of .said Yrelays Without operating saidmarginal relay and-means for closing a direct current .circuit over said line to operate said marginal .relay,.said signal. receiving means further lcomprising .an alternating current source, a rst .phase detectorV including a polarized relay, phase `control means coupling saidY alternatingr current source to :said .rst dc'- tector, and means coupling said source .to one of the conductors of said line, said signal transmitting means further comprising .means including impedance elements for varying the phase-of the alternating current in said one conductor, means for impressing 0n the inputV circuit of said detector a voltage derived from the voltage impressed on said oneY conductor to operate the polarized relay of said first detector .in one direction` when the alternating .current of said conductor is of onephase andto .operate said .polarized` relay in the other direction when. the alter.- nating current in saidgconductor is of a diierent phase, said signal receiving means further com.- prising a secondphasedetector includingV a po.-- larized relay, phase controlmeans coupling. said alternating current source to said second detec.- wrlf means lCoupling Said. source to. the other Conductor 0f Said. line Said` signal transmitting.. means further comprising means `including .ima

pedance elements Yfor varying the phase of the alternating vcurrent in said other conductor, means for impressing on-the input circuit of said seconddetector a voltage derived 4from the voltage impressed onsaid other vconductor to operate the polarized relay of said second detector in one direction when Vthe alternating current in said other conductor is of one phase and to operate the polarized relay of said second detector in the other .direction when the alternating .current in said other conductor is of a different phase, and signal register means selectively controlled by said signaland polarized relays.

5. In a signaling system, 'a two-conductor line, a source of '.directcurrent and a marginal signal relay atone end of said line, said source and relay connected in series across the conductors of said line, signal sending means at the other end .of'said line for completing a circuit for operating said relay, an alternating current generator at said o neend-of` said line, a networkfconnected to one of the conductors ofv said line at said one Aend, another network connected to the other of the conductors of .said line yat said one end, means coupling Lsaid generator to said conductors and networks, a first phase detector comprisinabalancesi rectiers. and a. polarized relay, means Comprising phase `conical, means coupling said generator to said Iirst detector, a second phase detector comprising balanced rectiiiers and a polarized relay, means comprising Dhae control means coupling said generator tosaid second detector, a transformer having .its primary Winding connectedin parallel vwith said rst conduc- I tor and in 1parallel with said .first network land having its secondary winding connected Ain the input circuit of the .rectiers of said vfirst detector, a second vtransformer having 4its primary winding connected in `parallel with the other conductorof saidline :and in parallel with said :second network and having its secondary winding connected in the input circuit of vthe rectiiiers of said second detector, means comprising .an induction coil anda condenser vat the other end of .the line connectedgin series withvsaid one .conductor,4 .means comprising an inductance coil and acondenser at said-other end of the line connected in series with, said other conductor, signaling sending ,means for short-circuiting the induction coil-connected to said -iirst conductor, signal sending means for short-circuiting theinducl'Iioncoil connected to said other conductor, thenetworl and phase control means Yassociated with saidoneconductor being-of such a character that thepolarizedrelay o f said iirst detector is energizediin one direction when the'associated induction coil is included .in the circuit through said. one conductqr` vand energized in 'the other direction when .the associated inductionY coil is short-circuited and-A the network and phase conf.. trol means associated; .,'th Seid other Conductorbeing of such -a characterthat the I,polarized.relay 0f Said .second detector is energized in om: direction when the inductioncoil-associated with said other conductor isvinclu'ded inthe circuit through. Said other Conductor andenersized in the other directOIlWhQn .the induction coil as- Scented; with. Said. Vother conductor. is short-cir.- Quiiedi Vandsignal resister :meanssselectivelyConf trolled yby said marginal and zpolarvizedarelays.

6.- In a signaling systemes line, Signalleirinemeansonnestedzto one eedfof Saidrlinefsi anal traosmittinsfmeans G filfnf.wird` to the-Other end.

0..f Said line, said.. Signal.- reeiving/mean. 500m.- Dif-,isms a `sono@ Qidrgt Current and' afpluf rality of signal relays connected in series across the conductors of said line, one of said relays loeing a sensitive relay operated Whenever a loop circuit is closed over said line and the others of said relays being marginal relays, said signal transmitting means comprising means for closing a direct current circuit over said line to selectively operate said relays, said signal receiving means further comprising an alternating current source, a rst phase detector including a polarized relay, phase control means coupling said alternating current source to said iirst detector, and means coupling said source to one of the conductors of said line, said signal transmitting means further comprising means including impedance elements for varying the phase f the alternating current in said one conductor, means for impressing on the input circuit of said detector a voltage derived from the voltage impressed on said one conductor to operate the polarized relay of said first detector in one direction when the alternating current of said conductor is of one phase and to operate the polarized relay in the other direction when the alternating current in said conductor is of a diierent phase, said signal receiving means further comprising a second phase detector including a polarized relay, phase control means coupling said alternating current source to said second detector, means coupling said source to the other conductor of said line, said signal transmitting means further comprising means including impedance elements for varying the phase of the alternating current in said other conductor, means for impressing on the input circuit of said second detector a voltage derived from the voltage impressed on said other conductors to operate the polarized relay of said second detector in one direction When the alternating current in said other conductor is of one phase and to operate the polarized relay of said second detector in the other direction when the alternating current in said other conductor is of a diierent phase, and signal register means selectively controlled by said signal and polarized relays.

7. In a signaling system, a two-conductor line, signal receiving means connected to one end of said line and comprising an alternating current source, a first phase detector including a rst signal relay, means coupling said alternating current source and rst detector and one of the conductors of said line to eiiect the operation oi said rst signal relay when the alternating current in said one conductor is of one phase but not when the alternating current in said one conductor is of the opposite phase, a second phase detector including a second signal relay, means coupling said alternating current source and said second detector and the other conductor of said line to effect the operation of said second signal relay When the alternating current in said other conductor is of one phase but not when the alternating current in said other conductor is of the opposite phase, a source of direct current and other signal relays including a marginal relay connected in series with said source across the conductors of said line, signal transmitting means connected to the other end of said line and comprising selective means for varying the magnitude of the direct current in said line, for Varying the phase of the alternating current in one of the conductors of said line, for varying the phase of the alternating current in the other of the conductors of said line, for varying the magnitude of the direct current and at the same time the phase of the alternating current in either one of the conductors of said line, for varying the phase of the alternating current in both of the conductors of said line at the same time or for varying the magnitude of the direct ycurrent in said line and at the same time the phase of the alternating current in both of the conductors of said line, thereby to eect the selective operation of one or more of controlled by said signal relays.

KENNETH? W. PFLEGER. 

